240 CHEMISTRY OF PLANT LIFE 



the activities of the plant which produces them, or to influence the 

 physiological activities of other plants with which these substances 

 come in contact through either the parasitic or the symbiotic 

 relation, have been variously discussed under the names 

 "hormones," "auximones," and "vitamines"; while injurious 

 substances are generally known as " toxins. " Whether these 

 different terms actually represent different definite types of sub- 

 stances, or whether there are actually different groups of stimu- 

 lating or inhibitory agents produced in plants, is uncertain; but 

 the following brief statements will serve to indicate the general 

 nature of the suggestions which have been put forward and of 

 the experimental work which is now in progress. 



HORMONES 



The term " hormone " was first used to designate certain 

 stimulating substances which are supposed to exist in the 

 intestinal tracts of animals and to cause the glands to elaborate 

 and secrete their characteristic enzymes. The supposed " hor- 

 mones " are not themselves active in performing the digestive 

 functions of the glandular secretions, but are the exciting, or stim- 

 ulating, agents which cause the glands to secrete their active' 

 enzymes. 



The same term has been used, by certain plant physiologists, 

 to designate any agency, either external or internal, which stimu- 

 lates plant protoplasm to abnormal activity. It has been pointed 

 out that there are a variety of substances, which are themselves 

 chemically neutral, that are powerful stimulants of vital activity 

 if used in only minute proportions, but are powerful poisons if 

 present in larger amounts. Many of the alkaloids act in this 

 way upon the animal organism; while chloroform, toluene, and 

 even some of the more complex hydrocarbons, act similarly upon 

 the tissues of plants, and ether vapor is known to be a powerful 

 stimulant in accelerating the flowering of plants and the ripening 

 of fruits. It has been shown that the vapors of all such sub- 

 stances readily penetrate the protoplasm of leaves, seeds, etc., 

 even when the same parts are impermeable to most mineral salts, 

 sugars, etc. ; and that upon entrance to the protoplasm of a leaf, 

 or a seed, they tremendously stimulate its metabolic activity. 



